Background: It has been proposed that the weight loss associated with glucagon-like peptide-1 receptor agonists (GLP-1 RAs) may improve the detection of breast cancer in patients undergoing this treatment. Thus, this study aimed to determine whether the weight-lowering effects of GLP-1 RAs is associated with an increased detection of breast cancer among obese women with type 2 diabetes. Methods: Using the United Kingdom Clinical Practice Research Datalink, we conducted a propensity score-matched cohort study among female obese patients with type 2 diabetes newly-treated with antidiabetic drugs between 1 January 2007 and 31 January 2018. New users of GLP-1 RAs (n=5,510) were matched to new users of second- to third-line non-insulin antidiabetic drugs (n=5,510). Time-dependent Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of breast cancer associated with different GLP-1 RA maximal weight loss categories (<5%, 5%-10%, >10%). Results: Breast cancer incidence gradually increased with GLP-1 RA maximal weight loss categories, with the highest HR observed for patients achieving at least 10% weight loss (HR: 1.77, 95% CI: 1.12, 2.81). In secondary analyses, the HR for >10% weight loss was highest in the 2-3 years since treatment initiation (HR: 2.90, 95% CI: 1.21, 6.92). Conclusions: In this population-based study, the detection of breast cancer gradually increased with GLP-1 RA weight loss categories, particularly among those achieving >10% weight loss. These results suggest that significant weight loss with GLP-1 RAs may improve the detection of breast cancer among obese patients with type 2 diabetes.